[
https://issues.apache.org/jira/browse/TRAFODION-3042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16451364#comment-16451364
]
ASF GitHub Bot commented on TRAFODION-3042:
-------------------------------------------
GitHub user zellerh opened a pull request:
https://github.com/apache/trafodion/pull/1539
[TRAFODION-3042] RAND() function is not always random
When called without a seed, we use a seed based on the system timestamp.
The random generator we use generates similar output values for seeds that are
close together. Adding another randomization step to avoid that.
Also switched from a microsecond to a nanosecond-based timestamp.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/zellerh/trafodion bug/R23a
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/trafodion/pull/1539.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #1539
----
commit 36e21b2c9c722bbcb551c35a761f069811051ea0
Author: Hans Zeller <hzeller@...>
Date: 2018-04-24T21:39:16Z
[TRAFODION-3042] RAND() function is not always random
When called without a seed, we use a seed based on the
system timestamp. The random generator we use generates similar
output values for seeds that are close together. Adding another
randomization step to avoid that.
commit 4f834729efa2c9ae74922f1f32226a29b6f8d7d0
Author: Hans Zeller <hzeller@...>
Date: 2018-04-24T22:01:37Z
[TRAFODION-3042] Switch to nanosecond-resolution time
Getting ready for the day where we can do two RAND() calls
in a microsecond - hopefully soon :-)
----
> RAND() function is not always random
> ------------------------------------
>
> Key: TRAFODION-3042
> URL: https://issues.apache.org/jira/browse/TRAFODION-3042
> Project: Apache Trafodion
> Issue Type: Bug
> Components: sql-exe
> Affects Versions: 2.2.0
> Reporter: Hans Zeller
> Assignee: Hans Zeller
> Priority: Major
>
> When trying the RAND() function, I found that it does not always behave as I
> would expect. I tried this example:
> {noformat}
> >>select rand(), rand(), rand() from dual;
> (EXPR) (EXPR) (EXPR)
> ---------- ---------- ----------
> 78242471 78511383 78612225
> --- 1 row(s) selected.
> >>select rand(), rand(), rand() from dual;
> (EXPR) (EXPR) (EXPR)
> ---------- ---------- ----------
> 1589208276 1589460381 1589561223
> --- 1 row(s) selected.
> >>select rand(), rand(), rand() from dual;
> (EXPR) (EXPR) (EXPR)
> ---------- ---------- ----------
> 134371215 134724162 134858618
> --- 1 row(s) selected.
> >>
> {noformat}
> So, it seems that if we call rand() within a very short time, the value will
> be non-random.
--
This message was sent by Atlassian JIRA
(v7.6.3#76005)
